Core Java - Interview Questions and Answers for 'Core Java' | Search Interview Question

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Q1031. Can you name few Java packages which you frequently used ?

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Q1032. How does encoding affect using Reader / writer classes or Stream classes in Java ?

Core Java

Ans. Which group of bytes represent which character is defined by character encoding. So when reading character by character from a stream of bytes using Reader, specifying character encoding becomes significant as the same group of bytes can represent different character in different character encoding(Eg UTF-8 and UTF-16 etc.)

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Q1033. How executor service is better than using primitive Threading mechanism using Thread class or runnable Interface ?

Core Java

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Q1034. What is the difference between TreeSet and TreeMap ?

Core Java

Ans. TreeSet contains only values as elements whereas TreeMap contains Key value pairs.

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Q1035. Which of the following is insertion heavy - HashSet or TreeSet ?

Core Java

Ans. TreeSet as it needs elements in a particular order

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Q1036. Write a Program to print a pattern ?

Core Java

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Q1037. Have you used Java 8 Lambda expressions ?

Core Java

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Q1038. How to calculate string length without using inbuilt function

Core Java

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Q1039. What is the difference between abstraction and abstract class ?

Core Java

Ans. Abstract class is one of the facility for achieving abstraction in Java.

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Q1040. Write code to print a Pyramid pattern ?

Core Java

Ans. public static void printTriagle(int n)
{
// outer loop to handle number of rows
// n in this case
for (int i=0; i1; j--)
{
// printing spaces
System.out.print(" ");
}

// inner loop to handle number of columns
// values changing acc. to outer loop
for (int j=0; j<=i; j )
{
// printing stars
System.out.print("* ");
}

// ending line after each row
System.out.println();
}
}

// Driver Function
public static void main(String args[])
{
int n = 5;
printTriagle(n);
}

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Q1041. What does System.exit() do ?

Core Java

Ans. Generally used to indicate termination

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Q1042. How to sort objects based on one of the field ?

Core Java

Ans. Using comparable and comparator and sorted collections like TreeSet or TreeMap.

or

use stream api from java 8 onwards which internally refers to comparable and comparator through lambda expressions

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Q1043. Can we have interface as a replacement for utility class ?

Core Java

Ans. Yes, With Java 8 we can use Interfaces as collection of utility methods through the use of default methods.

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Q1044. What are custom annotations and How can we create one ?

Core Java

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Q1045. What is the difference between scope and access modifiers ?

Core Java

Ans. Scope modifiers changes the scope of a particular element or a method. For ex - static changes the scope of that of class and not of object.

Access modifiers changes the access priviledges of a particular element or a method. For ex - private , public etc.

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Q1046. Why Java has final class ?

Core Java

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Q1047. Which memory segment is cleaned by Garbage Collection - stack or heap ?

Core Java

Ans. Heap as objects are stored ink heap.

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Q1048. Do we have references for the objects that are eligible for garbage collection ?

Core Java

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Q1049. Are final methods faster than regular instance methods ?

Core Java

Ans. Yes. As they cannot be overridden , there is no use of virtual table concept which is used for dynamic binding resolution.

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Q1050. What is virtual table with respect to method overriding in Java ?

Core Java

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Q1051. How is the virtual method table implemented in Java?

Core Java

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Q1052. How many VTables are there for each class ?

Core Java

Ans. There is one VTable for each class.

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Q1053. Have you ever used java.util.Objects class ?

Core Java

Ans. Yes, We are using requireNonNull method for validating if the object is null.

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Q1054. Why do we use getbytes in Java?

Core Java

Ans. It is used to convert String into an array of bytes.

byte[] getBytes() - converts String into a byte array.

byte[] getBytes(Charset charset) - converts String to byte array, based on charset encoding.

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Q1055. Can Java be run on hardware with just the JVM and no OS ?

Core Java

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Q1056. Which java feature is used to convert primitive type to reference type ?

Core Java

Ans. AutoBoxing

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Q1057. What is a reflexive equals contract ?

Core Java

Ans. An equal contract is said to be reflexive is equality between 2 objects always returns to be true.

For example -

Object o1;
Object o2;

o1.equals(o2); // returns true
o2.equals(o1); //returns true

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Q1058. Explain Transitive equals contract.

Core Java

Ans. The equals contract is said to be transitive if

obj1.equals(obj2); and obj2(.equals(obj3)

then obj1.equals(obj3) also returns true.

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Q1059. How will you enable or disable assertion for a package during runtime ?

Core Java

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Q1060. Which java version supports assertion ?

Core Java

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